This invention relates to a photo-curable epoxy resin composition, and more particulaly to a photo-curable epoxy resin composition which has been improved in curing characteristics and which provides a cured product having suitable electric characteristics for use as insulating and resist material in electric equipment.
Recently, a process for hardening a resin by the use of a light is attracted attention to save energy and improve operating efficiency in the field of resins. Among others, processes for photo-curable the epoxy resins are regarded as important because of wide range of their possible applications. In a process for photo-curing an epoxy resin, the epoxy resin itself is very important, besides the curing conditions. Thus, compositions having various formulations have widely been studied. The photo-curable epoxy resin compositions, which have hitherto been known to the art, can roughly be classified into two groups.
One is an epoxy resin which has been modified by using a photo-polymerizable compound containing a vinyl group or vinyl groups, such as acrylic acid and its derivatives. However, photo-cured products obtained from the modified epoxy type resins have the defects that heat resistance is considerably inferior to that of photo-cured products obtained from epoxy resins themselves.
The other is an epoxy resin which is added a photo-decomposable catalyst and is to be cured by the catalyst. As the photo-decomposable catalyst used for the purpose, there may be mentioned the complex having the following formula: ##STR1## wherein Ar represents a phenyl group; X represents an iodine atom, a sulfur atom or a diazo group; and Y represents BF.sub.4, PF.sub.6, AsF.sub.6 or SbF.sub.6.
[See, for example, Macromolecules, Vol. 10, 1307 (1977); Journal of Radiation Curing, Vol. 5, 2 (1978); Journal of Polymer Science, Polymer Chemistry Edition, Vol. 17, 2877 (1979); Ibid. Vol. 17, 1047 (1979); Journal of Polymer Science, Polymer Letters Edition, Vol. 17, 759 (1979); Japanese Provisional Patent Publication No. 65219/1980; U.S. Pat. No. 4,069,054; and British Pat. Nos. 1,516,511 and 1,518,141.]
In case of the epoxy resin compositions which are added the photo-decomposable catalysts, obtained photo-cured products show good mechanical and thermal characteristics. In this case, however, the catalyst components remain as ionic impurities in the photo-cured products so that when such photo-cured products containing the ionic impurities are used in electric equipment, it has the problems that the ionic impurities adversely affect the electric characteristics of the photo-cured products such as an electric insulation ability and sometimes cause an electric equipment or the like to corrode.
It is an object of this invention to provide a photo-curable epoxy resin type composition which may eliminate the above-mentioned disadvantages and has good storability under room temperature and cool-and-dark place, quickly hardens with irradiation of light, particularly of ulraviolet rays, and can be heat-cured at a temperature of not less than 150.degree. C., and gives a cured product containing no ionic impurities, causing no corrosion of a metallic material which is contacted with the cured product and having excellent electrical characteristics.